1. Field of the Invention
The present invention relates to a heat exchanger, a system for utilizing the waste heat from an internal combustion engine via a Clausius-Rankine cycle process, and an internal combustion engine having a system for utilizing the waste heat of the internal combustion engine by the Clausius-Rankine cycle process.
2. Description of the Background Art
Internal combustion engines are used in various technical applications for converting thermal energy into mechanical energy. In motor vehicles, especially in trucks, internal combustion engines are used to move the motor vehicle. The efficiency of internal combustion engines can be increased by the use of systems for utilizing the waste heat from the internal combustion engine by means of the Clausius-Rankine cycle process. In this process, the system converts the waste heat from the internal combustion engine into mechanical energy. The system comprises a circuit having lines with a working medium, e.g., water or an organic refrigerant such as R245fa, a pump for conveying the working medium, an evaporator heat exchanger for vaporizing the liquid working medium, an expander, a condenser for liquefying the vaporous working medium, and a collecting and equalizing tank for the liquid working medium. The use of systems of this type in an internal combustion engine can increase the overall efficiency of an internal combustion engine in an internal combustion engine with a system of this type as an internal combustion engine component.
In the evaporator heat exchanger, the working medium is vaporized by the waste heat of the internal combustion engine and then the vaporized working medium is supplied to the expander, where the gaseous working medium expands and performs mechanical work by means of the expander. In the evaporator heat exchanger, for example, the working medium is conveyed through a first flow duct and exhaust gas from the internal combustion engine through a second exhaust gas flow duct. As a result, the heat is transferred from the exhaust gas with a temperature in the range between 400° and 600° C. to the working medium in the evaporator heat exchanger and thereby the working medium is converted from the liquid state to the vapor state.
WO 2009/089885 A1, which corresponds to US 20100319887, which is incorporated herein by reference, shows a device for exchanging heat between a first and a second medium, having plate pairs stacked one on top of another in a stacking direction, whereby a first flow space, through which a first medium can flow, is formed between the two plates of at least one plate pair and a second flow space, through which a second medium can flow, is formed between two plate pairs, adjacent to one another, whereby the first flow space has a first flow path for the first medium with flow path sections which can be flown through one after the other in opposite directions and are separated from one another by a partition wall arranged between the at least two plates of the at least one plate pair.
In an evaporator heat exchanger in a plate/sandwich structure, spacers are arranged between the plate pairs. In this regard, high temperature changes occur in the evaporator heat exchanger during operation of a system for utilizing the waste heat of an internal combustion engine. High requirements are imposed on the operating life of the evaporator heat exchanger when used in an internal combustion engine of a truck. The evaporator heat exchanger in this case must stand up to an operating life of more than 10 years or a mileage of the truck of more than 1 million kilometers. High temperatures occur in this regard in the evaporator heat exchanger, because exhaust gas with high temperatures in the range of 600 to 800° C. is introduced into the evaporator heat exchanger, so that temperatures in the range of up to 500 to 800° C. occur in the evaporator heat exchanger. As a result, the evaporator heat exchanger is exposed to high thermal loads. Spacers are arranged between the plate pairs. The spacers and the plate pairs are soldered together, so that as a result high stress occurs between the spacers and the plate pairs (on the plate pairs/spacers), whereby two spacers each are arranged on a side of a plate pair. Such high shear stress leads to leaking and thereby to a limited operating life of the evaporator heat exchanger.